When my best friend Judy turned 40, she organised a group of us to fly to New York. As the plane was ready to take off, three members of security approached me. "Madam, we'd like to escort you off the plane," the manager said. "We think you've had too much to drink." "Honestly, I haven't had a drop," I protested. They apologised and left me – but I wanted the plane to swallow me up. It had been the same situation when I arrived at the boarding gate, feeling tired and a little dizzy. "Excuse me, have you been drinking?" a cabin attendant asked. She wouldn't even let me on board without inspecting my bottle of water and my breath. The truth is I drink very little alcohol nowadays, but people often assume I'm drunk.

I was working for Estée Lauder when I first began losing my balance, and a colleague advised me to see a doctor. I had suddenly found it difficult to walk in a straight line, but as the symptoms were mild and only worsened with tiredness, I hadn't thought much of it. While undergoing medical tests to find out what was wrong, I left my job to follow my dream of setting up my own mobile makeup business in Aberdeen. It flourished, but doctors were still baffled by my lack of balance. Could it be MS? In April 2001, a genetic specialist from Edinburgh did some blood tests and I was diagnosed with type six ataxia.

Ataxia is a genetic disorder that causes a loss of co-ordination, and can leave speech slurred; in essence, sufferers appear drunk. I had never heard of it when I was diagnosed, and it is still little known. So when I was banned from entering a bar with my best friend last Christmas, it didn't shock me that the doorman wasn't convinced by the medical card I carry everywhere. I had left my walking stick at home and leant on my friend's arm for support. Although completely sober, we were forced to leave because the doorman felt I had "had enough". Meanwhile, boisterous rugby fans celebrating a win were welcomed.

When I was diagnosed, I was a fit 31-year-old who ran at least five miles a day. I loved the freedom and adrenaline of running – turning all the day's work stresses into something positive. My partner of 10 years was sociable like me, and we'd see friends every night. But the diagnosis was like a dark cloud over us. Although my symptoms were mild – only my balance was affected– we knew it was a progressive condition, and were warned that we would need multiple tests if we wanted children. Six months later, my partner said the relationship wasn't working and left for work overseas the next day. I'll never know if it was the ataxia that split us up, but I've always wondered.

I put all my energy into my business and didn't tell anyone at work about my illness. I was invited to work at London fashion week in 2004. Most people didn't notice there was anything wrong with me and my heart soared. But within a year, everything changed. My ataxia worsened and the incident on the plane knocked my confidence. Although I had to stop running years before, I ended up closing my business in 2006. I feel fine – it's not my symptoms that are the problem – but anyone who sees me assumes I am intoxicated. I slur my words most of the time, and my lack of balance is much more obvious than it used to be. I'm still capable of applying makeup – my hands are as steady as ever – but who wants to be made up by someone who is swaying from side to side? There are have been other consequences too; I have decided not to have children because I don't want to pass this condition on, and anyway I am not sure I will meet anyone else.

Yet I have learned to live with my condition. I go to the gym every day – and have a personal assistant to guide me once a week. I love cooking and just have to be extra careful I don't drop anything. I seldom drink so I am as in control of my ataxia as I can be. My friends have been brilliant, and I always tell people in public situations about my condition so they don't make a wrong assumption.

Three weeks ago I got a new job as a disability housing officer. It's given me a real boost and now I try to accept what I can do – not what I can't.